The present invention relates to a movable magnet type instrument for operating a pointer and an instrument device using this movable magnet type instrument.
For example, the movable magnet type instrument of a crossing coil type is generally known as an instrument main body applied to an instrument device for a vehicle. Such a movable magnet type instrument is also called as an air core movement, and a rotor magnet magnetized by two poles of N and S poles is stored into a space formed in a housing. A rotor shaft fixed to the rotor magnet is pivoted by the housing. Further, one end of the rotor shaft is projected to the exterior of the housing, and the pointer is mounted. A pair of coils is orthogonally wound around the outer circumference of the housing. Driving signals having electrical angles different from each other, concretely, voltage signals of sine and cosine waves having different phases at the electrical angles are supplied to each coil. The rotor magnet is pivotally rotated by a synthetic magnetic field generated by each coil by this supply of the driving signal. The pointer can be angularly moved in accordance with a measuring amount by controlling the supply of the driving signal to each coil in accordance with a measured amount such as a vehicle speed, an engine rotation.
In such a movable magnet type instrument, a main portion of the movable magnet type instrument is covered with a shield case constructed by a magnetic material such as an iron nickel alloy such that no rotor magnet magnetized by the two poles is influenced by earth magnetism.
In the above movable magnet type instrument, the shield case constructed by the magnetic material such as the iron nickel alloy is required in consideration of magnetic interference with the rotor magnet, etc., magnetic efficiency, etc. Therefore, the number of parts cannot be reduced and it is difficult to reduce cost since the magnetic material such as the iron nickel alloy forming the shield case is expensive.
Further, in the instrument device called a combination meter, plural movable magnet type instruments mentioned above are particularly arranged. Therefore, the cost of the above movable magnet type instrument is further added to the cost of the instrument device as it is, so that the cost of the instrument device is increased.
In view of this point, a main object of the present invention is to provide a movable magnet type instrument able to reduce cost and an instrument device using this movable magnet type instrument.
The present invention resides in a movable magnet type instrument comprising a rotor magnet magnetized such that adjacent magnetic poles are poles different from each other; a pair of coils arranged around this rotor magnet and having winding central axes crossing each other without being perpendicular to each other; control means for processing an input signal based on a measured amount and supplying a driving signal mutually having a different electrical angle to each of said coils and rotating and operating said rotor magnet; and a pointer for rotating said rotor magnet as a driving source; wherein, when the number of magnetic poles of said rotor magnet is set to n and an acute angle formed by crossing said winding central axes is set to r, the acute angle r is set to an angle calculated by 360/2n (n is a multiple of 2 equal to or greater than 4).
Further, a protecting cover for protecting said coils and constructed by a nonmagnetic material is arranged.
Further, transmitting means for transmitting rotation of said rotor magnet to said pointer is arranged between said pointer and said rotor magnet, and said pointer is decelerated and rotated through said transmitting means in comparison with said rotor magnet.
The present invention also resides in an instrument device using at least one movable magnet type instrument and comprising a rotor magnet magnetized by at least four magnetic poles or more, a pair of coils arranged around this rotor magnet and having winding central axes crossing each other without being perpendicular to each other, and a pointer rotated with said rotor magnet as a driving source; wherein the instrument device has at least one movable magnet type instrument in which, when the number of magnetic poles of said rotor magnet is set to n and an acute angle formed by crossing said winding central axes is set to r, the acute angle r is set to an angle calculated by 360/2n (n is a multiple of 2 equal to or greater than 4).
Further, a protecting case for protecting said coils and constructed by a nonmagnetic material is arranged in said at least one movable magnet type instrument.
Further, transmitting means for transmitting rotation of said rotor magnet to said pointer and decelerating and rotating said pointer in comparison with said rotor magnet is arranged between said pointer and said rotor magnet in said at least one movable magnet type instrument.